The present invention relates to a system and a method for vaporized fuel processing as well as a medium recording a program for performing the method.
A vaporized fuel processing system is well known in which vaporized fuel from a fuel tank is charged into a canister for adsorption by causing the fuel tank to communicate with the canister, and vaporized fuel released from the canister is purged into an induction system of an internal combustion engine in a predetermined operating condition, and a technique described in a patent literature No. 1 can be raised as an example of the vaporized fuel processing system.
[Patent Literature No. 1] JP-A-9-151812
In the technique described in the patent literature No. 1, a vacuum or negative pressure is introduced into a vaporized fuel processing system including a canister by opening a purge control valve, as well as an atmosphere-vented (open to the atmosphere) valve, and an accumulated value for each pressure change when the negative pressure so introduced is maintained is calculated, whereby whether or not an abnormality such as leakage of vaporized fuel is occurring in the vaporized fuel processing system is checked based on the accumulated values so calculated. Note that while the technique described in the patent literature No. 1 discloses the construction for relieving the pressure in the canister, the pressure relief is carried out in order to check on the leakage of vaporized fuel only and there is disclosed no attempt to increase the purge efficiency.
Incidentally, in recent years, as emission control regulations are strengthened, while the purge flow rate of vaporized fuel needs to be increased as high as possible, since driving conditions for purging are limited, there exists a limitation on the increase in purge flow rate. Consequently, it is desired to increase the purge efficiency by increasing the purge density.